Process for producing a semiconductor device

ABSTRACT

A semiconductor device having a large-capacitance capacitor in which an insulator film is formed underneath a film made of a material having a high dielectric constant, such as tantalum oxide, in such a manner that a portion of the insulator film underneath a defect region which is undesirably thin is thicker than other portions of the insulator film, thereby preventing occurrence of a failure in terms of dielectric strength and deterioration of the lifetime of the capacitor which would otherwise be caused by the existence of the defect region. Also disclosed is a process for producing such semiconductor device. Thus, it is possible to effectively prevent occurrence of problems which would otherwise be caused when a material having a high dielectric constant, such as tantalum oxide, is employed as a dielectric film of a capacitor, so that the reliability of a semiconductor having a large-capacitance capacitor is greatly improved.

This application is a Divisional application of application Ser. No.07/247,343, filed Sept. 21, 1988, now U.S. Pat. No. 4,937,650, which isa continuation application of application Ser. No. 936,603, filed Dec.1, 1986, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a processfor producing the same. More particularly, the present inventionpertains to a semiconductor device having a capacitor of largecapacitance and high reliability and a process for producing suchsemiconductor device.

As is well known, one type of capacitor in which a silicon dioxide filmis used as an insulator film is widely employed in various kinds ofsemiconductor memory.

As the packing density of semiconductor integrated circuits increases,the area for capacitors becomes considerably small. A reduction in thearea for capacitors decreases capacitance, and this leads to a loweringin reliability of the semiconductor memory. For this reason, a means hasalready been proposed in which an oxide of a transition metal having arelatively large dielectric constant, e.g., Ta₂ O₅, is employed as adielectric film of a capacitor in order to prevent lowering ofcapacitance.

For example, Japanese Patent Laid-Open No. 4152/1984 discloses a methodwherein, after a tantalum oxide (Ta₂ O₅) film has been formed on asilicon substrate, a heat treatment is carried out in a wet oxidizingatmosphere to grow a silicon dioxide film at the interface between thetantalum oxide film and the silicon substrate, and then an upperelectrode made of a refractory metal or a silicide of a refractory metalis formed on the tantalum oxide film to produce a capacitor.

However, the examination made by the inventor of this application hasfound that the capacitor produced by the above-described conventionalmethod is unfavorably inferior in terms of long-term reliability, andthe thickness of the silicon dioxide film formed between the tantalumoxide film and the silicon substrate is undesirably increased to lowerthe capacitance, thus considerably deteriorating effectiveness which isoffered by employment of tantalum oxide as a dielectric film.

More specifically, although the above-described prior art has theadvantage that formation of a silicon dioxide film between a siliconsubstrate and a tantalum oxide film enables a reduction in the defectdensity of the tantalum oxide film and consequently permits animprovement in dielectric strength, the capacitance per unit area isextremely decreased. Further, when the thickness of the silicon dioxidefilm exceeds 40 Å, it is impossible for the capacitor to obtain along-term reliability which is superior to that of the silicon dioxidefilm since the degradation in dielectric strength with time of thecapacitor in the case where a predetermined voltage is applied theretodepends on the durability of the silicon dioxide film at the interfacebetween the silicon substrate and the tantalum oxide film.

SUMMARY OF THE INVENTION

In view of the above-described problems of the prior art, it is anobject of the present invention to provide a semiconductor deviceincluding a capacitor which has a reduced defect density, asatisfactorily high dielectric strength, an improved long-termreliability and a favorably large capacitance, and a process forproducing such semiconductor device.

To this end, according to the present invention, after an oxide film ofa transition metal has been formed on a silicon substrate or a lowerelectrode, a heat treatment is carried out in a dry oxidizing atmosphereto grow an oxide of the silicon substrate or an oxide of the lowerelectrode underneath a defect region of the oxide film of the transitionmetal in such a manner that the film thickness is greater at the defectregion than that at other regions. In this way, a total film thicknessof the defect region of the oxide film of the transition metal isincreased by the existence of the oxide of the lower electrode, andlowering of the dielectric strength is thereby prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view employed to describe the arrangement of thepresent invention;

FIG. 2 is a sectional view showing the structure of an SiO₂ filmproduced when no heat treatment is carried out;

FIGS. 3 to 6 are views employed to explain advantageous effects offeredby the present invention;

FIG. 7 is a sectional view showing one embodiment of the presentinvention;

FIGS. 8 and 9 show in combination another embodiment; and

FIGS. 10 and 11 are a sectional view and a histogram, respectively,which are employed to describe still another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described hereinafter by way of one of themost typical examples thereof in which a silicon substrate and tantalumoxide (Ta₂ O₅) are employed as a lower electrode and an oxide of atransition metal, respectively.

In a region which involves deterioration in dielectric strength of theinterface between a silicon substrate and a tantalum oxide film, thethickness of the tantalum oxide film is smaller than that of otherregions. According to the present invention, silicon dioxide isselectively grown at this defect region to increase the total filmthickness, so that the dielectric strength is improved and it ispossible to prevent deterioration in dielectric strength of thecapacitor. On the other hand, according to the examination made by thepresent inventors, when the thickness of the silicon dioxide filmexceeds 40 Å, the long-term reliability becomes lower than that in thecase of a film thickness of 40 Å or less. For this reason, in regionsother than the above-described defect region, the thickness of thesilicon dioxide film at the interface between the silicon substrate andthe tantalum oxide film is set at 40 Å or less, thus preventing loweringof the long-term reliability.

The silicon dioxide silicon film formed underneath a defect regionpartially has a thickness of 40 Å or more. In such case, however, sincethe silicon dioxide film is grown in such a manner that the defectregion has a satisfactorily larger dielectric strength than that inregions other than the defect region, the long-term reliability is notinferior to that of the other regions, as described later. Further,since the thickness of the silicon dioxide film in the defect region isincreased, the capacitance of this region is decreased. However, thearea of the defect region is extremely small as compared with the totalarea of the capacitor. Accordingly, there is substantially no effect onthe total capacitance of the capacitor, and the total capacitance istherefore substantially equal to the capacitance of regions other thanthe defect region. Since the silicon dioxide film formed in regionsother than the defect region has a thickness of 40 Å or less, it ispossible to realize an extremely large capacitance.

To form an SiO₂ film underneath the tantalum oxide film in such a mannerthat this portion of the SiO₂ is thicker than other portions thereof, itis necessary to carry out a heat treatment in a dry oxidizing atmosphereafter the tantalum oxide film has been formed. If the heat treatment iscarried in a wet oxidizing atmosphere, a relatively thick SiO₂ film willbe formed not only underneath the defect region but also the wholeinterface between the tantalum oxide film and the silicon substrate,which means that it is impossible to obtain a large capacitance.

Also, as the above-described lower electrode, a polycrystalline siliconfilm or a silicide film such as titanium silicide may be employed inaddition to a silicon substrate.

It is also possible to attain the object of the present invention byemploying titanium nitride or aluminum (or an aluminum-based alloy) andcarrying out a heat treatment in a dry oxidizing atmosphere to form atitanium oxide film or an aluminum oxide film underneath a defect regionof the tantalum oxide film in such a manner that the formed film isthicker at the defect region than at other regions, in a manner similarto that in the case of employing silicon.

Embodiment 1

FIG. 1 is a sectional view of a capacitor formed in such a manner that,after a tantalum oxide film 3 has been formed on the surface of asilicon substrate 1, a heat treatment is carried out in a dry oxidizingatmosphere at 800° C. to 1000° C. to form a silicon dioxide film 2 atthe interface between the tantalum oxide film 3 and the siliconsubstrate 1, and then a tungsten film 4 which serves as an upperelectrode is deposited on the tantalum oxide film 3.

The thickness of the silicon dioxide film 2 formed at the interfacebetween the silicon substrate 1 and the tantalum oxide film 3 depends onthe thickness of the tantalum oxide film 3 and the temperature of theheat treatment carried out in a dry oxidizing atmosphere. Therelationship therebetween will be explained below with reference to FIG.3. In the graph shown in FIG. 3, the axis of abscissas represents thethickness of the tantalum oxide film 3 formed on the silicon substrate1, and the axis of ordinates represents the thickness of the silicondioxide film 2 formed by the heat treatment at the interface between thetantalum oxide film 3 and the silicon substrate 1. As will be clear fromthe graph, when the heat treatment temperature is 800° C., if thethickness of the tantalum oxide film 3 exceeds 10 nm, substantially nosilicon dioxide is grown at the interface, but as the thickness of thetantalum oxide film 3 decreases below 10 nm, the thickness of thesilicon dioxide film 2 increases. Similarly, when the heat treatmenttemperature is 1,000° C., the thickness of SiO₂ film which is formedunderneath a tantalum oxide film having a thickness of about 10 nm ormore is about 2 nm or less, but as the thickness of the tantalum oxidefilm decreases below 10 nm, the thickness of the SiO₂ film formedthereunder increases suddenly.

Accordingly, if, after a tantalum oxide film has been formed on asilicon substrate or a lower electrode, a heat treatment is carried outin a dry oxidizing atmosphere, an SiO₂ film 2 is formed in such a mannerthat the film 2 is relatively thick underneath defect regions (portionshaving relatively small film thicknesses) of the tantalum oxide film 3but is relatively thin underneath normal regions (portions havingrelatively large thicknesses), as shown in FIG. 1. As a result, loweringof dielectric strength, which is caused by the fact that tantalum oxidefilm 3 is locally thin, is effectively prevented, and a capacitor ofextremely high reliability is formed.

FIG. 2 shows a cross-sectional structure of a capacitor formed in such amanner that, after a tantalum oxide film has been formed, an upperelectrode 4 is formed without carrying out a heat treatment such as thatdescribed above.

As will be clear from FIG. 2, if the above-described heat treatment isnot carried out, a relatively thin SiO₂ film 2' which has a uniformthickness is formed. This SiO₂ film 2' is a natural oxide film ofsilicon, and it is slightly oxidized when a tantalum oxide film isformed by sputtering in an oxidizing atmosphere. Since the SiO₂ film 2'has a thickness of only about 1.5 nm, the laminate of dielectric filmsin each of the defect regions (portions in which the tantalum oxide film3 has a relatively small thickness) has an unsatisfactorily small totalthickness (the sum of the respective thicknesses of the tantalum oxidefilm 3 and the SiO₂ film 2'), and this constitutes a cause ofdeterioration of dielectric strength.

If the heat treatment, which is effected after the formation of atantalum oxide film, is carried out in a wet oxidizing atmosphere, anexceedingly thick SiO₂ film will be formed not only underneath defectregions but also at the whole interface between the tantalum oxide filmand the lower electrode, which means that it is impossible to obtain alarge capacitance.

Accordingly, it is necessary to carry out a heat treatment in a dryoxidizing atmosphere after a tantalum oxide film has been formed, toform the SiO₂ film 2 partially differing in thickness between thetantalum oxide film 3 and the lower electrode 1 as shown in FIG. 1.

As described above, the tantalum oxide film 3 involves undesirably thinportions (defect regions) which are locally present therein, andtherefore, if the SiO₂ film formed at the interface is relatively thinand uniform, the dielectric strength of each of the portions of thetantalum oxide film 3 which have relatively small thicknesses islowered, and the reliability is degraded.

The feature of the present invention resides in that an SiO₂ filmpartially differing in thickness is formed at the interface between atantalum oxide film and a lower electrode by a heat treatment which iscarried out in a dry oxidizing atmosphere. In this case, the respectivethicknesses of the tantalum oxide film and the SiO₂ film are essentialto the present invention and therefore will be explained below indetail.

Referring to FIG. 2, a tantalum oxide film 3 having a thickness of 75 Åis formed on the lower electrode by carrying out a heat treatment at800° C. for 30 minutes. As described above, the tantalum oxide film 3formed on the surface of the silicon substrate 1, serving as a lowerelectrode, is not uniform in thickness and involves portions which arethinner than 75 Å. In this case, as shown in FIG. 3, an SiO₂ film havinga thickness of about 0.5 nm is grown underneath the tantalum oxide film3 having a thickness of 75 Å by the above-described heat treatment.Therefore, the total thickness of the SiO₂ film, including the SiO₂ filmwhich has been formed before the above-described heat treatment, isabout 2.0 nm. According to the present invention, a heat treatment iscarried out after the tantalum oxide film has been formed. Effectsproduced by a heat treatment carried out in an oxidizing atmosphere willbe explained below with reference to the graph shown in FIG. 4 whereinthe axis of ordinates represents effective electric field and the axisof abscissas represents the thickness of tantalum oxide film. In thiscase, the effective electric field is a value obtained by dividing thevoltage applied to the capacitor by a thickness of silicon dioxide filmwhich is equal to the capacitance per unit area of a double layer filmconsisting of a tantalum oxide film and a silicon dioxide film, that is,electric field converted into the thickness of silicon dioxide.Referring to FIG. 2, in the case where the heat treatment according tothe present invention is not carried out, when an effective electricfield of 13 MV/cm is applied to a region in which the thickness of thetantalum oxide film 3 is 75 Å, an electric field higher than 13 MV/cm isundesirably applied to a region in which the thickness of the tantalumoxide film 3 is smaller than 75 Å. For example, an effective electricfield of about 19 MV/cm is undesirably applied to a region in which thethickness of the tantalum oxide film 3 is 20 Å. On the other hand, inthe case where a heat treatment is carried out in an oxidizingatmosphere at 800° C. for 30 minutes, when an effective electric fieldof 13 MV/cm is applied to a region in which the thickness of thetantalum oxide film is 75 Å, an effective electric field which is lowerthan 13 MV/cm is applied to a region in which the thickness of thetantalum oxide film is smaller than 75 Å. For example, as shown in FIG.3, an SiO₂ film having a thickness of about 40 Å is grown by theabove-described heat treatment in a region in which the thickness of thetantalum oxide film is 20 Å, and therefore the applied effectiveelectric field is only about 8 MV/cm. Accordingly, effective dielectricstrength is improved in a portion in which the tantalum oxide film islocally thinned.

FIG. 5 shows results of measurement carried out as to the long-termreliability of a capacitor in which a dielectric film is defined by adouble layer film consisting of a tantalum oxide film and a silicondioxide film. FIG. 5 shows average lifetimes of capacitors measured byapplying a predetermined electric field thereto. As will be clear fromFIG. 5, capacitors in which the thickness of the silicon dioxide filmformed at the interface between the tantalum oxide film and the siliconsubstrate exceeds 50 Å are readily broken down, whereas capacitors inwhich the thickness of the silicon dioxide film is 40 Å or less havemuch longer lifetimes than the former. Accordingly, in a capacitor inwhich a double layer film consisting of a tantalum oxide film and asilicon dioxide film is employed as a dielectric film, it is possible toobtain extremely favorable results by setting the thickness of thesilicon dioxide film at 40 Å or less.

FIG. 6 shows results of measurement of the time to failure of capacitorsin which a double layer film consisting of a tantalum oxide film ofthickness 75 Å and a silicon dioxide film formed at the interfacebetween a silicon substrate and the tantalum oxide film is employed as adielectric film. In the measurement an effective electric field of 13MV/cm was applied to such capacitors with the thickness of the silicondioxide film varied within a range from 20 Å to 60 Å. As will be clearfrom FIG. 6, as the thickness of the silicon dioxide film decreasesbelow 40 Å, the time to failure suddenly increases. This is because, asthe thickness of the silicon dioxide film decreases, the electronconduction mechanism is allowed to include more direct tunnelingcomponents, so that it becomes difficult for the silicon dioxide film tobe damaged and broken down. Similar results were obtained also in thecase where the tantalum oxide film has a thickness other than 75 Å.

Accordingly, portions of the silicon dioxide film which are formedunderneath regions of the tantalum oxide film other than defect regionspreferably have a thickness of 40 Å or less.

As shown in FIG. 4, in a region in which the thickness of the tantalumoxide film 3 is less than 40 Å, the thickness of the silicon dioxidefilm 2 formed at the interface between the tantalum oxide film 3 and thesilicon substrate 1 exceeds 40 Å. However, the effective electric fieldapplied to this region is less than 9.5 MV/cm, as will be clear fromFIG. 4. In this case, the lifetime is longer than 10⁵ seconds as shownin FIG. 5, which is not inferior to that of a region in which thethickness of the tantalum oxide film is 75 Å. Accordingly, even when asilicon dioxide film having a thickness of 40 Å or more is formedunderneath a defect region of the tantalum oxide film, there is no fearof the dielectric strength and average lifetime being lowered. It hasbeen found that similar advantageout effects are obtained with an oxideof Ti, Hf, Nb or Zr in addition to tantalum oxide.

Embodiment 2

This embodiment provides the example of a semiconductor device having acapacitor of excellent reliability in which the lower electrode is madeof polycrystalline silicon and which can be formed on an isolationinsulator film or an element region.

FIG. 7 is a sectional view of a memory cell having a storage capacitorand a transfer transistor. In FIG. 7, the reference numeral 5 denotes aP-type silicon substrate, 6 a gate insulator film, 7 a field insulatorfilm, 8, 9 n⁺ regions defining a source and a drain, 10 apolycrystalline silicon film defining a first electrode (lowerelectrode) of the capacitor, 4 a tungsten electrode, 12 an intermediateinsulator film, and 11 an aluminum wiring. In addition, numerals 13 and14 respectively denote first and second word lines made ofpolycrystalline silicon. The aluminum wiring 11 defines a bit line. Inthe memory cell arranged as described above, the first electrode of thestorage capacitor is defined by the polycrystalline silicon film 10 onwhich is formed a dielectric film defined by a double layer filmconsisting of a tantalum oxide film 3 and a silicon dioxide film 2. Asshown in FIG. 7, the tantalum oxide film 3 is locally thinned, andportions of the silicon dioxide film 2 which are located underneaththese thin regions of the film 3 are thicker than the other portionsthereof. Portions of the silicon dioxide film 2 underneath regions ofthe tantalum oxide film 3 other than the thin regions have a thicknessof 40 Å or less. The capacitor having the tungsten film 4 as its upperelectrode shows characteristics equal to those of the capacitor inaccordance with Embodiment 1 which is formed on the silicon substrate.As shown in FIG. 7, since the capacitor in accordance with thisembodiment can be formed on the element region (transfer transistor) orthe element isolating insulator film region (the thick SiO₂ film 7), itis extremely useful for producing a high-packing density memory.

Similar advantageous effects are also found using an oxide of Ti, Hf, Nbor Zr in addition to tantalum oxide.

Embodiment 3

Referring to FIG. 8, a tantalum oxide film 3 and an upper electrode 4defined by a tungsten film are formed on a silicon substrate having asteep step on the surface thereof by a known sputtering method, therebyforming a capacitor. Thus, a portion of the tantalum oxide film 3 whichis formed on the side of the step is smaller than a horizontal portionof the film 3 and therefore readily gives rise to a failure in terms ofdielectric strength.

However, if, after the Ta₂ O₅ film 3 has been formed at the stepportion, annealing is effected in a dry oxidizing atmosphere at 900° C.,an SiO₂ film 2 is formed at the interface between the Ta₂ O₅ film 3 andthe silicon substrate 5 in such a manner that a portion of the film 2 isthicker at the thin side portion of the Ta₂ O₅ film 3 than underneaththe horizontal portion of the film 3. Therefore, it is possible toprevent deterioration in dielectric strength of the Ta₂ O₅ film 3 at theside portion thereof and consequently obtain a higher dielectricstrength than that of the capacitor shown in FIG. 8. On the other hand,the portion of the SiO₂ film 2 which is formed at the interface betweenthe horizontal portion of the Ta₂ O₅ film 3 and the Si substrate 5 isextremely thin, so that the capacitance of the horizontal portion of thecapacitor is substantially equal to that of the capacitor shown in FIG.8. Thus, it is possible, according to the present invention, to form acapacitor having a large capacitance, improved reliability and asatisfactorily high dielectric strength even in a stepped region on asilicon substrate.

Embodiment 4

This embodiment employs a titanium nitride (TiN) film as the lowerelectrode of the capacitor, whereas the above-described embodimentsemploy a silicon substrate or a polycrystalline film as the lowerelectrode of the capacitor.

Referring to FIG. 10, the reference numeral 1 denotes a siliconsubstrate, 15 a TiN film defining a first electrode of the capacitor, 16a titanium oxide film, 3 a tantalum oxide film, and 4 a tungsten filmdefining a second electrode of the capacitor. In this embodiment, a TiNfilm 15 having a thickness of 500 Å is first formed on the siliconsubstrate 1 by a known reactive sputtering method using an N₂ -Ar gasmixture and Ti as a target. A tantalum oxide film 3 having a thicknessof 100 Å is formed on the TiN film 15 by a known reactive sputteringmethod using an Ar-O₂ gas mixture and tantalum as a target. Thereafter,a heat treatment is carried out is a dry oxidizing atmosphere at 600° C.In consequence, a titanium oxide film 16 is grown at the interfacebetween the tantalum oxide film 3 and the TiN film 15 serving as thefirst electrode. Then, a second (upper) electrode 4 constituted by atungsten film is formed on the tantalum oxide film 3 to produce acapacitor. As shown in FIG. 10, the tantalum oxide film 3 has a thinregion, and a portion of the titanium film 16 underneath the thin regionis thicker than other portions thereof. Accordingly, this thin regionconstitutes no cause of deterioration of dielectric strength. If nooxidizing treatment were carried out, no thick titanium oxide film wouldbe formed underneath the thin region, and this region would lead todeterioration of dielectric strength. FIG. 11 shows a histogram forcomparison as to dielectric strength between a case where theabove-described oxidizing treatment is carried out after the formationof the tantalum oxide film and a case where no oxidizing treatment iscarried out. As will be clear from FIG. 11, the dielectric strength isgreatly improved by carrying out the oxidizing treatment. Since thedielectric constant of titanium oxide is larger than that of SiO₂, if atitanium oxide film is employed as a part of the dielectric film of thecapacitor, the degree to which the capacitance is lowered is so smallthat it can be ignored, and this is also greatly advantageous. It shouldbe noted that the range of preferable heat treatment temperatures in thecase of employing TiN is from 500° to 800° C. NbN or TaN may be employedas the lower electrode in place of TiN. In such case also, thedielectric strength and long-term stability of the capacitor can beconsiderably improved by carrying out a heat treatment in a dryoxidizing atmosphere at 500° to 800° C. after the formation of thetantalum oxide film. It is also possible to obtain excellent results byemploying aluminum or an aluminum-based alloy (e.g., an aluminum-siliconalloy) as the lower electrode and carrying out the above-described heattreatment at 300° to 500° C. In addition, it is possible to employ asthe lower electrode of the capacitor various kinds of silicide, e.g.,tantalum silicide, tungsten silicide, molybdenum silicide or titaniumsilicide. The range of preferable heat treatment temperatures in suchcase is substantially the same as that in the case of employing a singlecrystal silicon substrate or a polycrystalline silicon film, that is,from 600° to 1,000° C. Within this temperature range, it is possible toobtain excellent results. It is, as a matter of course, possible toemploy as the upper electrode (second electrode) various kinds ofmaterial employed to form an electrode or wiring, such as Al, Al-basedalloy (e.g., Al-Si alloy), polycrystalline silicon, W, Mo, W-silicide,Ta-silicide, Mo-silicide and Ti-silicide. The atmosphere in which theabove-described heat treatment is carried out preferably has a watervapor content of about 1,000 ppm or less. When the water vapor contentin the atmosphere is excessively high, a thick oxide film is undesirablyformed also underneath portions other than a defect portion as describedabove, whereas, when the water vapor content is set at 1,000 ppm orless, favorable results can be obtained.

As will be clear from the above description, it is possible, accordingto the present invention, to considerably increase the capacitance of acapacitor without lowering the dielectric strength and long-termstability thereof. Accordingly, the present invention is extremelyuseful for improvement in packing density of semiconductor integratedcircuits.

What is claimed is:
 1. A process for producing a semiconductor device,comprising the steps of:forming a first dielectric film on a firstelectrode; carrying out a heat treatment in a dry oxidizing atmospherehaving a water vapor content of 1,000 ppm or less, to form a seconddielectric film between said first electrode and said first dielectricfilm in such a manner that said second dielectric film is relativelythick underneath a relatively thin portion of said first dielectric filmand is relatively thin underneath a relatively thick portion of saidfirst dielectric film; and forming a second electrode on said firstdielectric
 2. A process according to claim 1, wherein said firstdielectric film is formed by sputtering.
 3. A process according to claim1, wherein said first electrode is defined by either a single crystalsilicon substrate or a polycrytalline silicon film, said heat treatmentbeing carried out at a temperature of from 600° C. to 1,000° C.
 4. Aprocess according to claim 1, wherein said first electrode is asilicide, said heat treatment being carried out at a temperature of from600° C. to 1,000° C.
 5. A process according to claim 4, wherein saidsilicide is selected from the group consisting of tantalum silicide,tungsten silicide, molybdenum silicide and titanium silicide.
 6. Aprocess according to claim 1, wherein said first electrode is defined byany one of a titanium nitride film, a neodymium nitride film and atantalum nitride film, said heat treatment being carried out at atemperature of from 500° C. to 800° C.
 7. A process according to claim1, wherein said first electrode is defined by either an aluminum film oran aluminum-based alloy film, said heat treatment being carried out at atemperature of from 300° C. to 500° C.
 8. A process according to claim1, wherein said first dielectric film is made of a material selectedfrom the group consisting of tantalum oxide, titanium oxide, hafniumoxide, neodymium oxide and zirconium oxide.
 9. A process according toclaim 1, wherein the relatively thin portions of the second dielectricfilm are formed to have a thickness of 40 Å at most.
 10. A processaccording to claim 9, wherein said first dielectric film is made of amaterial selected from the group consisting of tantalum oxide, titaniumoxide, hafnium oxide, neodymium oxide and zirconium oxide.
 11. A processaccording to claim 10, wherein said first electrode is defined by eithera single crystal silicon substrate or a polycrystalline silicon film,said heat treatment being carried out at a temperature of from 600° C.to 1,000° C.
 12. A process according to claim 10, wherein said firstelectrode is a silicide, said heat treatment being carried out at atemperature of rom 600° C. to 1,000° C.
 13. A process according to claim12, wherein said silicide is selected from the group consisting oftantalum silicide, tungsten silicide, molybdenum silicide and titaniumsilicide.
 14. A process according to claim 10, wherein said firstelectrode is defined by any one of a titanium nitride film, a neodymiumnitride film and a tantalum nitride film, said heat treatment beingcarried out at a temperature of from 500° to 800° C.
 15. A processaccording to claim 10, wherein said first electrode is defined by eitheran aluminum film or an aluminum-based alloy film, said heat treatmentbeing carried out at a temperature of from 300° C. to 500° C.
 16. Aprocess according to claim 9, wherein the relatively thick portions ofthe second dielectric film are formed to have a thickness of at least 40Å.
 17. A process according to claim 1, wherein the first dielectric filmis provided on a step, with portions of the first dielectric filmprovided on a vertical part of the step being relatively thin ascompared to portions of the first dielectric film provided on ahorizontal part of the step.